The Asian Football Confederation charged Kawasaki Frontale with discrimination on Thursday after their fans raised a controversial wartime Japanese flag during a midweek Asian Champions League match in South Korea.

According to article 58.3 of the AFC's disciplinary and ethics code, the team could face a minimum penalty of playing two matches in an empty stadium plus a fine of at least $15,000.

The club were notified of the decision through the Japan Football Association. The AFC will give Frontale an opportunity to respond before making a final decision on the penalty before Kawasaki's next ACL match at home to Hong Kong's Eastern SC on May 9.

Frontale, who can qualify for the round of 16 with a win over Eastern, are holding onto hope that the sanctions will not be severe.

"Just looking at what we could face seems tough," a Kawasaki media officer said. "But we will try to deal with (the AFC) as well we can. We do not think the disciplinary code is the be all and end all."

J-League Chairman Mitsuru Murai said he does not believe the fans were politically motivated, but added they need to be mindful of their actions at games.

"The important thing is players as well as fans and supporters should be feeling safe at stadiums, and we need to work to ensure that kind of environment," Murai said.

In Kawasaki's 1-0 win at Suwon Bluewings on Tuesday, two Frontale supporters waved the 16-ray rising sun flag, nearly provoking a post-game riot.

Kawasaki officials confiscated the flag from the two fans and had to escort other supporters out of the stadium.

The flag was used by the Imperial Japanese Army during World War II. Although it is still flown by the Japan Maritime Self-Defense Force, the flag is considered a symbol of Japan's wartime aggression in many Asian countries, including South Korea and China.